1. Field of the Invention
The present invention relates to a structure of a tire for a motorcycle.
2. Description of the Related Art
In recent years, a motorcycle can carry out high speed running and the size and weight have been increased. This is caused by an increase in the amount of exhaust from the engine. For this reason, an enhancement in the performance of the tire for the motorcycle (the realization of a high straight running stability and a high cornering stability) has increasingly been required in order to withstand the high speed running of the motorcycle.
In the motorcycle, a body is greatly inclined during cornering. Therefore, the tire for the motorcycle is also inclined and rolled with respect to a road surface. Accordingly, the tire for the motorcycle is to be designed in such a manner that a cornering force and a camber thrust are properly generated.
In the case in which only the cornering of the motorcycle is taken into consideration, a shoulder portion in the tire for the motorcycle is set to have a high stiffness. Consequently, stable cornering can be implemented. In the tire for the motorcycle, however, the stiffness of a tread portion is generally improved with an enhancement in the stiffness of the shoulder portion. Consequently, in the case in which the motorcycle carries out straight running, there is a tendency that the stiffness of the tread portion of the tire for the motorcycle is excessively increased so that the straight running stability of the motorcycle is deteriorated.
Under such circumstances, conventionally, the tire for the motorcycle has been required to maintain the high stiffness of the shoulder portion and a more reduced stiffness of the tread portion (particularly, a central part) as compared with the shoulder portion.
For this reason, various improvements have conventionally been made for the structure of the tire for the motorcycle.
In a tire for a motorcycle which has conventionally been provided in order to obtain the compatibility of the straight running stability with the cornering stability, an enhancement in the stiffness of the shoulder portion is not always balanced with a reduction in the stiffness of the tread portion so that the straight running stability and the cornering stability are not always compatible with each other at a high level. Moreover, the structural unification of the tread portion and the shoulder portion is not always achieved. For this reason, a running condition for a transition period from straight running to cornering (or from the cornering to the straight running) holds a linearity with difficulty.